(1) Field of the Invention
The present invention relates to a fixture for integrated circuit to test. More particularly, the present invention relates to a parallel test fixture for mixed signal integrated circuits.
(2) Prior Art
Generally speaking, the various kinds of semiconductor integrated circuits (ICs) requiring such testing include analog signal ICs, digital signal ICs, and mixed signal ICs. Examples of analog signal ICs include amplifiers, voltage regulators, clock circuits, and phase lock loops. Digital signal ICs include high-speed very large scale integrated (VLSI) circuits such as microprocessors, microcontrollers, and digital signal processors, for example. Mixed signal ICs combine analog and digital functionality on a single semiconductor substrate or “chip,” and mixed signal ICs are used in several areas such as communications (both wireless and wire-based) in which digital data elements are converted into analog signals which are eventually transmitted.
Usually, automatic test equipment (ATE) for testing ICs has a fixture for being an interface between the ATE and the ICs (or device under test (DUT)). The fixture is utilized to connect several pins of the ATE and the corresponding pins of the ICs for transferring signals. A test signal is provided by the ATE to the ICs through the fixture for testing, and a tested signal of the ICs is transferred back to the ATE for checking the quality of the ICs.
FIG. 1 shows a diagram of a traditional system for testing mixed signal IC. The test method comprises a test signal provided by an ATE 101 and the test signal is transferred to a fixture 102. Then, the test signal is transferred from the fixture 102 to a DUT. In this case, the DUT is a mixed signal IC 103. Because the DUT is a mixed signal IC 103, the test signal has to be divided to an analog signal and a digital signal by the fixture 102 when testing the mixed signal IC 103. Therefore, the test signal would be divided to an analog signal to connect the analog signal of the mixed signal IC 103 and a digital signal to connect the digital signal of the mixed signal IC 103 by the fixture 102 for testing. After testing, tested signals are a tested analog signal and a tested digital signal of the mixed signal IC 103 to the fixture 102. Then, these tested signals would be integrated by the fixture 102. The integrated tested signal would be transferred from the fixture 102 to the ATE 101 for analyzing.
Generally speaking, the fixture 102 is a multi-layer printed circuit board (PCB). Because the fixture 102 for testing mixed signal IC, the stacked pattern design of the multi-layer PCB comprises an analog signal layer for transferring analog signal and a digital signal layer for transferring digital signal. However, the analog signal layer and the digital signal layer have to share a ground layer if the multi-layer PCB only having a ground layer. Then, several problems such as crosstalk and noise between the analog signal and the digital signal would be occurred. For solving these problems, when designing stacked pattern of the multi-layer PCB, an analog signal ground layer for connecting the analog signal layer to form a circuit and a digital signal ground layer for connecting the digital signal layer to form a circuit would be considered. This means the problems about noise and crosstalk could be solved by dividing the analog signal with the digital signal when testing.
However, the fixture mentioned-above only could test one mixed signal IC at one time, and it's very uneconomic for today. But, the fixture mentioned-above for a plurality of mixed signal ICs to parallel test, the different analog signals of different mixed signal ICs would cause noise or crosstalk each other and the different digital signals of the different mixed signal ICs also would cause noise or crosstalk each other. In order to solve these problems, the usually solving method is to add the ground layers when designing the stacked pattern of the multi-layer PCB. Then, each analog signal of each mixed signal IC is connected to each analog signal ground layer, and each digital signal of each mixed signal IC is connected to each digital signal ground layer in the multi-layer PCB. For example, if a fixture for testing four the same mixed signal ICs at one time, the design of the stacked pattern of the multi-layer PCB has to comprise four analog signal ground layers and four digital signal ground layers for solving the problems about inaccurate test results due to noise and crosstalk between each signal.
As mentioned-above, the thickness of the multi-layer PCB would be added if the numbers of layer of the multi-layer PCB. When testing more numbers of mixed signal ICs at one time, the numbers of layer of the multi-layer PCB of the fixture have to be more. Then, the design of the stack pattern of the multi-layer PCB would be more difficult and complicated.
Therefore, it's needed to find a fixture, which is a fixture for mixed ICs to parallel test. Moreover, the fixture not only solves the problems of crosstalk but also reduces the numbers of ground layers of the multi-layer PCB.